Conventionally beam pumps, or rod pumps, commonly known as pumpjacks, reciprocate a polished rod extending axially through a stuffing box which contains packing to seal against the polished rod. Further, rotary pumps rotate a rod within the stuffing box. In each case, the seal prevents wellbore fluids from leaking from the wellhead during movement of the rod. If the rod is not axially aligned within the bore of the stuffing box, excessive wear of both the packing and the rod can occur. In extreme cases of wear the rod can fail and drop into the wellbore, leaving the wellbore open to the surface. Misalignment may occur for many reasons such as resulting from settling of the pumpjack or rotary drive on a base or due to misalignment of the wellhead or stuffing box during assembly thereof.
Conventionally, it is known to provide a self-aligning stuffing box to assist in preventing polished rod failure. U.S. Pat. No. 3,887,196 to Renfrow, U.S. Pat. No. 4,889,184 to Lugtmeier and U.S. Pat. No. 6,412,783 to Finnestad all teach self-aligning stuffing boxes incorporating embodiments of a first tubular member having a convex face for engaging a concave seat on a second tubular member forming an alignment aspect therebetween, permitting limited universal movement of the first and second members relative to one another for aligning of the polished rod therein while maintaining sealing of the packing about the polished rod. In each of these examples, the alignment aspect is positioned significantly below the packing in the stuffing box, necessitating a relatively tall stuffing box. Height of the wellhead may become problematic if insufficient bridle clearance is available between a pumpjack bridle and the wellhead, resulting in a shortened and less effective pumping stroke.
In the case of rod failure, many stuffing boxes are provided with a valve for sealing off the wellbore in the event of catastrophic failure of the rod. Typically, a valve, such as a flapper valve, is pivotally mounted in the bore of the stuffing box and is biased outwardly to engage the rod, such that if the rod drops into the wellbore, the valve is freed to rotate and seal the bore.
As is the case in U.S. Pat. No. 6,412,783 to Finnestad, many valves are positioned below the packing elements in the stuffing box and therefore, in order to replace or service the valves, the wellhead and stuffing box must be disassembled which is costly and time-consuming.
Others such as U.S. Pat. No. 4,889,184 to Lugtmeier have attempted to resolve the problems associated with positioning the valve lower in the stuffing box by positioning the valve adjacent the top of the stuffing box necessitating additional height to the stuffing box to incorporate the valve thereabove.
Ideally, what is required is a stuffing box capable of self-alignment for preventing undue wear of the packing and the rod moving therein that has a lower profile for maximizing the space between the wellhead or stuffing box and the pumpjack bridle in the case of a reciprocating pump or a rotary drive and the stuffing box in the case of a rotary pump. Further, it would be ideal to equip the shortened stuffing box with a valve for sealing the wellbore in the event catastrophic failure of the rod occurs.